1. Field of the Invention
The present invention relates to a camera that engages in a focusing operation through the contrast method by using an image-capturing signal provided by an image-capturing element.
2. Description of the Related Art
The AF methods adopted in cameras in the related art include the so-called contrast method. In the contrast method, an image of a subject is captured by an image-capturing element such as a CCD and the focus position is determined by using the image-capturing signal within the focus area. The image-capturing signal within the area are filtered through a band pass filter (BPF) and the components in the image-capturing signal that correspond to a predetermined spatial frequency band are extracted. Then, by integrating the absolute values of the extracted components within the area, a focus evaluation value to be used for the focusing operation is obtained. This focus evaluation value represents the contrast level, and the contrast is at its highest at the point at which the focus evaluation value peaks.
Namely, the peak position matches the focus position. The peak is ascertained by performing an operation which is known as a so-called hill-climbing (or scaling) focusing operation in the related art. In a continuous AF mode in which an AF operation is constantly performed regardless of whether or not the shutter release button is pressed halfway down, the hill-climbing focusing operation is executed over predetermined time intervals so as to set a focus on the subject at all times.
However, during the hill-climbing focusing operation, the focus evaluation value is calculated by driving the lens, a decision is made as to whether or not the focus evaluation value is the peak value and the same process is repeated if the focus evaluation value is not the peak value. When such a hill-climbing focusing operation is repeated frequently over the predetermined time interval, the battery becomes depleted quickly.
There is another problem with regard to the hill-climbing focusing operation in the related art in that when a relatively large change occurs in the subject, the misalignment between the lens position at the startup and the peak position becomes significant to result in a lengthy hill-climbing focusing operation.
In addition, it is desired that a focused picture can be photographed by performing the hill-climbing focusing operation described above while minimizing the battery power consumption.